The present invention relates to the production of zirconium phosphate/activated carbon adsorbents and more particularly to a novel and improved homogeneous adsorbent of zirconium phosphate and activated carbon.
The unique and valuable properties of zirconium phosphate adsorbents at high temperatures at both high and low pH values and in the presence of oxidizing and reducing agents has been well established. Zirconium phosphate, for example, is a useful inorganic ion exchanger which can be used in chromatographic techniques for the selective separation of, for example, alkali metals for use in the nuclear processing industry. Zirconium phosphate has particular advantage over other metal complexes because of its stable valence state and its recalcitrance to dissociate from the phosphate under variable reaction conditions. Also, zirconium phosphate is non-toxic and relatively inexpensive.
A practical problem in using of zirconium phosphate alone is its tendency to form colloidal gels when exposed to aqueous electrolytic solutions. Another problem in use of zirconium phosphate by itself is its porosity, that is, the internal surface area of zirconium phosphate is unstable. These problems have been overcome by depositing the zirconium phosphate or other zirconium salt on an inert carrier, such as activated carbon. Activated carbon is the carrier of choice because it is well suited as an ionic exchanger support due to its high surface area, its relatively inexpensive manufacturing costs, and its ability to exhibit some ion exchange behavior itself.
Prior techniques for preparing the zirconium phosphate/activated carbon adsorbents have involved the impregnation of activated or oxidized carbon with zirconium phosphate. The impregnation typically is accomplished by treating the activated or oxidized carbon with a water-soluble zirconium salt followed by the conversion of the deposited zirconium salt to its phosphate by washing with phosphoric acid. Such processes are limited by the available pore structure of the starting carbon and by the heterogenity of the product. Accordingly, only a limited amount, eg. up to about 15% by weight, of zirconium phosphate can be deposited on the carbon adsorbent. With specific reference to the preparation of such zirconium phosphate activated carbon adsorbents and their use, reference is made to the following citations:
1. Hungarian Pat. No. 11878 (1977) PA1 2. Akatsu et al. "Radiochemical study of adsorption behavior of inorganic ions on Zirconium Phosphate Silica Gel and Charcoal", J. Nucl. Sci. and Tech., 2, 141, 1965. PA1 3. Shiao, S. Y., Johnson, J. S. "Preparation of Activitated Carbons filled with hydrous Zr (IV) oxide" p. 143 USDOE Document ORNL-5816 (1982). PA1 4. Shiao, S. Y., et al., J. Inorg. Nucl. Chem (1982) PA1 5. Nagy, L. G. et al. "Preparation of Zirconium Phosphate on Support Material and its Application for the Sorption of Some Radioions", J. Radio and Chem., 58, 215-220 (1980). PA1 6. Amphlett, C. et al., J. Inorg. Nucl. Chem, 10, 69 (1969) PA1 7. Mohiuddin, G. Et al "Ion exchange behaviour of alkali metals on treated carbons" USDOE Document ORNL//MIT-351 (1983).
The present invention is directed to an improved method for preparing the activated carbon/zirconium phosphate adsorbents and to a resulting novel product.